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24 February 2017

First record of a potentially invasive mussel Mytella charruana in Manila Bay

Human
activities have, in many unprecedented ways, accelerated biological shifts and
nuances in our planet. Such is the case for ManilaBay
and its inhabitants. A slew of anthropogenic activities such as land and
sea-based transportation, sedimentation, fisheries, and reclamation and land conversion
has put the ecosystem at high risk for biological invasions.

Meet the
Charru mussel Mytella charruana, a newly
reported species in ManilaBay, which has been previously documented to be
invasive in Florida.
A team of researchers led by Dr. Benjamin Vallejo (University of the
Philippines Diliman) and SeaLifeBase staff, Jeniffer Conejar-Espedido
(University of the Philippines Los Banos) confirms its first recorded presence in
the area. Previously identified as Mytilus
spp., the bivalve was later identified via DNA barcoding to be Mytella charruana, suggesting its
phylogenetic position within the Perna clade.
Increasing trend in its abundance from 2014 to 2015 indicates likelihood of establishment
and probable competition with the native mussel Perna viridis.

What makes
the species different from Perna and Modiolus is its dark bluish to brown hue
and a bluish to purplish nacreous interior. It is also bigger
(average of 2.8 cm shell length) compared to another non-indigenous mussel in
the area, Mytilopsis, which only
grows to 1 cm SL.

Researchers
suggest it is likely to have been introduced via ballast water or through
fouled ship hulls. Since mytilids in general adapt and highly reproduce in
estuarine and coastal conditions, the persistence of M. charruana is likely.

The spat
was first observed at the start of southwest monsoon rainy season. Assuming it
has a similar life history profile as that of P. viridis, its introduction must have occurred between late April and
early May 2014. This suggests possible competition between the two species. The
increasing abundance of M. charruana
also indicates its establishment in ManilaBay, but this is yet to
be verified in succeeding years. How it could affect the populations of the
native P. viridus is, however, is unknown.
Further studies on the reproduction, ecology, community dynamics and population
genetics are recommended.